The purpose of this project is to develop the technology and methodology to perform micro spectrophotofluorometry in caged laboratory animals using miniature fiber optic probes. The technique will be used initially for microwashout studies of tumors in rats using intravenously injected fluorescein to investigate variations in tissue perfusion in the tumors. In the future, we hope to employ the technique to study metabolic behavior of tumors and pharmacokinetics in animals.